2. Butenes
Where they come
from
Gas Gas Naphtha
Natural Gas lwetI Oil
Catalytic and
Thermal Crack-
Process
n m
i
i
Hydrotreating
Naphtha
Steam
&--
Crackin
O
i
l Vacuum
Distillation
-
-
-
-
-
-
Ethylene Propene Acetylene Ethylene Fuel Gas Ethylene Propene CL- C5- Pyrolysis
Fraction Fraction Gasoline
, + I 112.2.1
CL-Riffinate C5- Raffinate
Ethylene 2-Butene
manufacture
Ratfinate I1
isobutene or n- Butenes n- and lsopentenes n-Pentenes
lsobutene Oligomers n- and lsobutane n- and lsopentanes n- and lsopentanes
3. Which C4 are obtained by steam cracking?
most valuable C4olefin source:
steam crackingof naphtha
As shown in Table 3-3, a significantly higher fraction of
butenes is obtained from steam cracking of naphtha than from
catalytic cracking of gas oil. Therefore naphtha steam cracking
is the more interesting technology for production of unsatu-
rated C4compounds.
decrease of total C4 and C4 olefins, but As the cracking severity increases, both the total yield of the
-
increase Of butadiene under high severity
cracking conditions (consequence of
desired higher C2H4 yield)
C4fraction and the proportion of butenes decrease, while the
proportion of butadiene increases due to its higher stability:
Table 3-3. Composition of Cq fractions from steam cracking of
naphtha and catalyticcracking of gas oil (in wt%).
Steam cracking Catalytic cracking
Cracked products Low High (FCC) zeolite
severity seventy catalyst
butadiene is stable even under high-
severity conditions (thermodynamically
favored because of the conjugation energy
- - __
of 3.5kcal ,mol)
14.7kJ
1,3-Butadiene 26 47 0.5
Isobutene 32 22 15
1-Butene 20 14 12
trans-2-Butene 7 6 12
cis-2-Butene 7 5 11
Butane 4 3 13
Isobutane 2 1 31
Vinylacetylene
Ethylacetylene ]2 ]2 ] -
1,2-Butadiene
In steam cracking, the yield of the C4 fraction parallels the
boiling range of the feedstock, beginning with 2-4 wt% from
ethane/propane, reaching a maximum of 10-12 wt% from
naphtha, and decreasing to 8-10 wt% from gas oil.
butane
but-1-ene
1-butene
isobutane
(E)-but-2-ene
trans-2-butene
(Z)-but-2-ene
cis-2-butene
2-methylprop-1-ene
isobutene
buta-1,3-diene
butadiene
4. Uses of butenes
Alkylation of aromatics for gasoline additives
Homo- and co-polymers (iso-butene, 1-butene)
Hydroformylation to C5 aldehydes and alcohols
Synthesis of MTBE
Dehydrogenation of n-butenes to butadiene
Thermolysis of isobutene to isoprene
5. How to separate C4 olefins
Distillation is not an option since boiling points are too close to one another
between –10 °C to 5 °C
Separation occurs in different steps
C4 mixture
separation of
butadiene
Raffinate I
separation of
isobutene
Raffinate II
6. How to separate butadiene
1) Chemical separation with [Cu(NH3)2]OAc (not competitive nowadays) ASSIGNMENT: Find
out why
PRINCIPLE: butadiene forms a complex with Cu(I) whereas the other C4
components do not. The complex can reversibly form pure butadiene.
2) Extractive distillation with Acetone, furfurol, acetonitrile, dimethyacetamide,
dimethylformamide, N-methylpyrrolidone
PRINCIPLE: butadiene is more soluble in the solvents above than the rest of the
fraction. Simplified reactor scheme:
Butadiene
+ C4*
C4* (Raffinate I)
solvent
Solvent + Butadiene
Butadiene
Solvent
degasser
Extraction
column
7. How to separate isobutene
1) Molecular sieving (not competitive nowadays) ASSIGNMENT: Find out why
PRINCIPLE: Linear C4 will adsorb in the pores of the zeolite (3-10 Å)
whereas branched ones will not.
2) Further chemical reactions:
- Reversible hydration to form t-butanol
- Reversible esterification to methyl t-butylether (MTBE to TBME)
- H+-catalyzed oligomerization to form di- and triisobutene
- Lewis acid-catalyzed polymerization to form polyisobutene
8. Reversible processes
hydration to form t-butanol
Acids: H2SO4 (50-60%), HCl, Acidic ion exchange resins
Regeneration of isobutene with SiO2/Al2O3 catalyst in liquid or gas phase
esterification to methyl t-butylether (MTBE)
Catalyst: Acidic ion exchange resin
Uses of MTBE: Increases octane number, reversible reaction not desired.
Raffinate II is subjected to isomerization of n-butenes to give isobutene, which
is further converted to MTBE.
+ H3O+
OH
+ MeOH O
[H+]
MTBE
9. Irreversible processes
H+-catalyzed oligomerization to form di- and triisobutene
Acid: H2SO4 or ion exchange resin
Simple technology but isomerization is a major side reaction
Lewis acid-catalyzed polymerization to form polyisobutene
Catalysts:
-BF3 (BASF, MW between 1000-2500) additive to fuels and lubricants
-AlCl3 (Cosden, MW between 200 - 2700) plasticizer, adhesives
2
[H+]
n
L.A.
n
10. Purification of Raffinate II
At this point we have a mixture of linear butenes and butanes.
A separation by reaction - e.g. by hydration - is not needed due to the
exclusive reactions of butenes. Butanes are inert.
Separation of n-butanes from n-butenes can be done by extractive distillation
and of the isomers of butene by distillation.
11. 1-butene
Important to have pure to get the polymer of poly-1-butene (PB-1), used as
blending material for polyethylene and polypropylene. It is used as is in flexible
packaging, compounding, pressure piping and hot melt adhesives.
Synthesis via:
1) dimerization of ethylene:
[Cat]: Ti(OR)4 + AlR’3
2) Oligomerization of ethylene and separation (see SHOP)
2
[Cat]
